Agricultural machines are increasingly equipped with more elaborate soundproof cabs in order to protect the operator from environmental influences. In such instances, the operator is provided with information on the machine status in different ways, for example, in the form of warning indicators for rotational speeds and the pressure of the hydraulic fluid. Due to the sound insulation of the cabin, the operator cannot monitor and control the function of the machine as well as with machines that have an open workstation, namely because the ability of the operator to perceive the noises caused by the flow of material being harvested through the machine is diminished.
BG 33 743 describes a device for mechanically examining working elements of a grape picking machine. The vibrations of the device are measured and displayed on an oscillograph.
It is also known (e.g., from EP 0 452 544 A) to provide combine harvesters with vibration sensors that sense the sound waves caused by lost grain. The signals of the vibration sensors are evaluated and used for displaying the loss portion. In this case, it is disadvantageous that the vibration sensor lies in and consequently impairs the flow of material.